template <class T> struct multiplies;

<functional>

Multiplication function object class

This class defines function objects for the multiplication arithmetic operation.

Generically, function objects are instances of a class with member function operator() defined. This member function allows the object to be used with the same syntax as a regular function call, and therefore it can be used in templates instead of a pointer to a function.

multiplies has its operator() member defined such that it returns the product of its two arguments.

This class is derived from binary_function and is defined as:

template <class T> struct multiplies : binary_function <T,T,T> {
  T operator() (const T& x, const T& y) const
    {return x*y;}
};

Objects of this class can be used with some standard algorithms such as transform or accumulate.

Members

T operator() (const T& x, const T& y)

Member function returning the product of its two arguments (x*y).

Example

// factorials (multiplies example)
#include <iostream>
#include <functional>
#include <numeric>
using namespace std;

int main () {
  int numbers[9];
  int factorials[9];
  for (int i=0;i<9;i++) numbers[i]=i+1;
  partial_sum ( numbers, numbers+9, factorials, multiplies<int>() );
  for (int i=0; i<9; i++)
    cout << numbers[i] << "! is " << factorials[i] << "\n";
  return 0;
}

Output:

1! is 1
2! is 2
3! is 6
4! is 24
5! is 120
6! is 720
7! is 5040
8! is 40320
9! is 362880

See also